The present invention relates to a medical system, a method of using the system, an elongated, electrically activated x-ray tube unit and a hollow catheter according to the preambles of the independent claims.
In general the present invention relates to connecting a miniature x-ray tube for in vivo use to an electrical power source. A miniature x-ray tube according to the invention is, for example, useful in applications for prevention of restenosis and for treating diseases, such as cancer, in a living body.
In treating stenosis in coronary arteries, a restenosis occurs in 30-60% of the cases. It is known that a treatment with beta- or gamma- (x-ray) radiation will decrease the occurrence of restenosis substantially.
Another example of an application of the present invention is treatment of cancer tumors where it is desired to deliver radiation locally.
Methods to apply the radiation to the site of treatment are presently subject to intensive research. Generally, a hollow catheter is inserted into the body, typically via an artery, in such a way that its distal end is placed near the site of treatment. A source of radiation attached to the distal end of an elongated member is inserted into the hollow catheter, and is forwarded until the radiation source is disposed at a proper position for radiating the site of treatment. In the specific case of treating cardiac vessels, the catheter is placed near the cardiac vessel tree (this catheter often called a xe2x80x9cguide catheterxe2x80x9d). A very thin wirexe2x80x94called guide wirexe2x80x94is then used to probe further and reach the site where treatment shall be performed. The therapeutic device is moved along this wire, i.e. by threading the device onto the guide wire. It obvious that the therapeutic device has to have a hole close to its distal end in order to do this.
For example, the use of radioactive pellets or balloons etc. as radiation source is known. Since this method has some drawbacks, such as the need for substantial efforts to control radiation in the environment outside the patient, the use of a miniature electrical x-ray tube including a cold cathode has been proposed. Such a tube may be switched on and off due to its electrical activation. An example of such a x-ray tube is described in the U.S. Pat. No. 5,854,822.
A conventional miniature electrical x-ray tube requires electrical conductors to connect the tube, i.e. its anode and cathode, to an external power supply. Conventionally, two conductors, one for the cathode and one for the anode of the tube are connected to the tube. FIG. 1 schematically illustrates an x-ray tube according to this prior art. One of the conductors 2 is connected to one of the electrodes, e.g. the anode 4, and the other conductor 6 is connected to the other electrode, e.g. the cathode 8. The distance between the conductors is approximately the same as the radius of the x-ray tube and a breakdown might occur if the used voltage is increased. The breakdown may also occur between the electrode 4 and the conductor 6. However, due to the small dimensions used, the outer diameter of the connecting cable is typically in the range of 1-5 mm when used for cancer treatment and less than 1.5 mm when used in cardiology, and the high voltages used, typically 20 kV, the probability for electrical breakdown between the connections to the tube is considerable. In FIG. 1 xe2x80x9cd1xe2x80x9d designates the distance between the conductors, and the distance xe2x80x9cd2xe2x80x9d designates the distance between the electrode 4 and the conductor 6.
The prior art device has to be sufficiently small to be able to enter for instance cardiac vessels. The maximum dimension in this case should be  less than 2 mm in diameter, preferably 1.5 mm in diameter. The breakdown over d2 is determined by the electrical properties of the insulating tube 11 that mechanically connects the two electrodes to each other and the distance between the electrode 4 and the conductor 6. The voltage applied over the electrodes should be some 20 kV in order to achieve radiation energies that are penetrating far enough into the body tissue to be treated. Further more, a safety margin must be applied, and therefore the design should be made so that one safely can apply say 30 kV over the distances d1 and d2.
There are few materials considered for the insulating tube wall 11 that could withstand the voltage needed. The tube wall material should also be impervious to gas diffusion, so that the vacuum needed inside the tube is maintained over a long period of time. Pyrolytic Boron Nitride (pBN) is described as a good choice, having reported breakdown voltages of some 200 kv/mm. However pBN is relatively brittle and may easily break. A mechanically stronger choice is Alumina, which has the drawback of having only 40 kV/mm breakdown. If Alumina is used in prior art configurations, the dimension must be increased to achieve the safety margin and thus the preferred diameter of 1.5 mm or less is hard to achieve.
FIG. 1 also illustrates the deflection of the electron beam 10 due to the vicinity to the other conductor 6 in a principal manner. The outer conductor 6 typically has a coaxial geometry.
WO-98/48899 relates to a miniature X-ray unit using a coaxial cable to connect the x-ray tube to the power source.
This means that the distance corresponding to the x-ray tube radius, together with the dielectric medium between the conductors, or electrode to conductor, is limiting for the voltage level that can be applied across the electrodes.
Therefore, there is a need for a novel way to connect an x-ray tube to a power source, designed to allow for higher voltage potential levels.
It is an object of the present invention to provide a device and a method for electrically connecting a miniature electrical x-ray tube to an external power source, allowing for improved voltage potential levels to be delivered to the x-ray tube, without having to increase the geometry and giving a wider choice of materials for the design of the miniature x-ray source be used that can improve the mechanical strength.
The above-mentioned object is obtained by a medical system, a method of using the system, an elongated x-ray tube unit and a hollow catheter according to the characterizing portions of the independent claims.
Preferred embodiments are set forth in the dependent claims.
Generally, according to the invention one of the conductors for supplying voltage to the x-ray tube is integrated with, or attached to, the hollow catheter used to provide a path for inserting the x-ray source. At the distal end of the hollow catheter, said conductor is exposed at the inside of the hollow catheter to exhibit a terminal surface. The electrical connection to the x-ray tube is at one end (the proximal end when inserted into the hollow catheter) connected to a single electric cable, while the other end (the distal end when inserted into the hollow catheter) is provided with a terminal end surface adapted to achieve an electrical connection to the terminal surface of the hollow catheter when completely inserted into said catheter.
A great advantage of the present invention according to the claims is that the x-ray tube unit with the radiation source need not be sterilized because it is inserted into the hollow catheter that has an open proximal end to receive the tube unit and a closed distal end. Therefore only the catheter needs to be sterilized in that the x-ray tube unit is never in contact with body tissue. Thus, x-ray tube unit itself may be reused without sterilization. This should be compared with prior art systems where the insertion catheter (or guide catheter) has an open distal end and where the radiation source unit is in contact with body tissue.
Another great advantage of the present invention is that, if, due to unforeseeable circumstances any part of or the whole x-ray tube is damaged in any way, no parts would be spread inside the body but would instead be kept inside the hollow catheter.
In a specific embodiment of the invention, a radiation shielding material is provided at or in the hollow catheter. The shielding material is selected to absorb radiation of lower energies to a higher extent than radiation of higher energies.